The invention relates to a tire, more specifically to a pneumatic tire capable of continued mobility in a deflated condition.
Various tire constructions have been proposed for pneumatic runflat tires, that is; tires which normally operate in an inflated condition but which also permit a limited operation in a deflated condition. These tire constructions are generally formed of one or more generally radial carcasses which are turned up around one or more bead wires arranged in each bead. To obtain the desired mobility in the deflated condition, many of these tires further employ sidewalls which are reinforced and thickened by interposing additional rubber layers between the carcasses or between the carcasses and the tire innerliner. An example of such a reference tire is shown in FIG. 1.
It is also important that a runflat tire remain seated on the rim during deflated operation. Many solutions have been proposed including mechanical bead locks, special rim profiles or bead wire bundles of elongated cross-section. In the last instance as shown in FIG. 1, the elongated bead wire bundle functions both to anchor the carcass in the bead to resist tensile forces developed in the carcass and to retain the bead on the rim seat during deflated operation. This dual function necessitates design compromises.
Tires having carcasses turned up around bead wires necessarily have a discontinuity at the radially uppermost extent of the turned up portion of one or more of the carcasses. When the turned up portion is axially positioned to the exterior of a median axis of the tire cross section, deformation of the bead portion due to loading the tire places the turned up portion in a state of compressive stress. This stress state and the aforementioned discontinuity lead to design constraints resulting in tire performance compromises between the inflated and deflated states.
U.S. Pat. No. 5,263,526 to Oare et al and U.S. Pat. No. 5,511,599 to Willard both relate to runflat tires with multiple carcasses wherein at least one carcass is turned up around bead wires. These references disclose different design solutions to treat the carcass discontinuity. Oare et al disclose a tire with two cord reinforced carcasses, both of which are turned up around the bead wires. At least one carcass turned up portion extends radially to the tire equator, and the lower sidewall portion includes multiple reinforcing plies. In this context, the term xe2x80x9ctire equatorxe2x80x9d defines the radial position corresponding the point of maximum width or axial extent of the exterior surface of the tire. Willard discloses a tire having three cord reinforced carcasses wherein one carcass terminates at the radially and axially inward extent of the bead, the second carcass being turned up around the bead and overlapped by the third carcass in the axially outward portion of the lower sidewall. Neither reference avoids a compressive stress in the turned up portion due to its position at the axially outward side of the bead structure. As a result, the geometry and arrangement of products in the bead region must be adapted to have good durability when these products are subjected to a tensile-compressive cyclic stress. Thus, a tire whose design removes these constraints will yield better overall levels of both inflated and deflated performance.
The tire of the invention has a unique outermost carcass path designed to maximize the extent of tensile stress in the sidewall and bead portions of the tire. The invention further provides a bead portion for anchoring the carcass or carcasses in the bead and for retaining the bead on the mounting rim during deflated operation, and said carcass anchoring also facilitates the maintenance of the desirable carcass profile.
The tire according to the present invention comprises at least one axially outermost carcass anchored in each side of the tire in ; bead, the bead having a base which is intended to be mounted on the tire""s design mounting rim, each bead being extended radially upward by a sidewall portion, the sidewall portions joining a tread portion wherein,
a median reference profile is defined by the locus of points corresponding to the median position between the axially innermost surface and axially outermost surface of the tire,
a rim reference point R in said bead is defined having an axial coordinate equal to one half the nominal width and a radial coordinate equal to one half the nominal diameter of the mounting rim,
a bead reference point Z is defined as the intersection of the outermost surface of the tire with a horizontal line offset radially outward a distance from the radial coordinate of the rim reference point R.
a tread reference point N is defined on the outermost surface of the tire at the junction between the tread and sidewall portions of tire,
a sidewall reference point P is defined on the outermost surface of the sidewall of the tire and located between said reference points Z and N;
wherein said at least one axially outermost carcass is disposed axially outward of said median reference profile for radial positions between said sidewall reference point P and said tread reference point N,
wherein said at least one axially outermost carcass intersects said median reference profile at a point Q, said point Q having a radial position between said reference point Z and said reference point P, and thereafter being disposed axially to the interior of said median reference profile for radial positions inward of said point Q;
wherein each axial coordinate of said at least one axially outermost carcass has a corresponding unique radial coordinate for each radial position inward of said sidewall reference point P, and
said tire further comprises a first bead reinforcement for anchoring said at least one carcass in the beads and a second bead reinforcement for providing retention of the beads on the mounting rim in a deflated condition.
The invention just described introduces a unique carcass path defined such that at least the axially outermost carcass first passes axially to the exterior of the median position between the axially innermost and outermost surfaces of the tire from a point at least at the junction of the tread portion with the tire sidewall portions to a specified point above the bead thereafter passing to the interior of the median profile. In this manner the extent of tensile stress in the axially outermost carcass is maximized throughout the sidewall and bead potions of the tire. The carcasses have a radially innermost extent terminating in the bead area without being turned up around bead wires. The carcasses of this invention are anchored in the beads by reinforcements laterally bordering the carcass so as to resist the tension developed in the carcass during inflated or deflated operation of the vehicle. This carcass anchoring reinforcement in the bead can include essentially circumferentially oriented cords or other reinforcements with or without cords. Compared to conventional tires intended for use only in the inflated state, tires intended for extended deflated operation impose additional design constraints to insure retention of the beads on the mounting rim during deflated operation. The present invention introduces a second bead reinforcement positioned axially outward of the carcass anchoring reinforcement of a prescribed geometry to provide adequate retention of the bead on the tire mounting rim during deflated operation, and also to permit easy mounting of the tire on a standard profile rim. The bead retention reinforcement of the invention can include any material suitable to resist the stresses and temperatures during vehicle operation, such as circumferentially oriented cords or filaments, metallic cables, elastomeric materials, fiber reinforced resin matrices and their equivalents.
In a preferred embodiment of the invention the tire has a single radially oriented cord reinforced carcass having a path in the tire sidewall and bead conforming to the teaching relative to the median axis of the tire thickness such that the extent of the sidewall and bead portions of the carcass that remain in tension during inflated or deflated operation is maximized. One or more crescent shaped reinforcing members are disposed in the tire sidewalls between the carcass and the axially innermost surface of the tire so that the tire sidewalls are capable of supporting vehicle forces and moments during deflated operation. To anchor the carcass in each of the beads, the carcass is bordered, on at least one side, in the axial direction by at least one winding of circumferentially oriented cords incorporating a rubber layer interposed between the carcass and the circumferentially oriented carcass anchoring cords. A bead retention reinforcement is located axially outward of the carcass and carcass anchoring reinforcement. A elastomeric bead filler is posed radially outward of the bead retention reinforcement and axially between the carcass and the axially outermost surface of the tire.
In a second embodiment of the invention the tire has at least two carcasses, the first being disposed axially and radially outward from the second carcass. The path of the outermost carcass conforms to the tension maximizing profile of the preferred embodiment. This embodiment has at least two crescent shaped reinforcing members with the first disposed between the first and second carcasses and the second between the second carcass and the radially innermost surface of the tire. In the bead area the two carcasses may have a common circumferential alignment or may follow adjacent circumferential alignments. Carcasses are anchored in the beads by at least one winding of essentially circumferentially oriented cords ax bordering the respective carcass. As in the first embodiment a bead retention reinforcement and an elastomeric bead filler rubber are employed.
In a third embodiment of the invention the tire has at least three carcasses, the first being disposed axially and radially outermost from the second and third carcasses, the third carcass being disposed axially inward from the second carcass. The path of at least the outermost carcass conforms to a tension maximizing profile similar to that of the preferred embodiment. This embodiment has at least three crescent shaped reinforcing members with the first of said members being disposed between the first and second carcasses, the second of said members being disposed between the second and third carcasses, and the third of said members being disposed between the third carcass and the radially innermost surface of the tire. The carcasses are anchored in the bead by at least one winding of essentially circumferentially oriented cords axially bordering the respective carcass. In this embodiment the second and third carcasses have a common circumferential alignment in the bead area, and the cord density of each of the second and third carcass layers is less than that of the first carcass layer. Alternatively, each of the three carcasses may follow adjacent circumferential alignments wherein the respective cord densities are independent of each other. As in the first embodiment a bead retention reinforcement and an elastomeric bead filler rubber are employed.